Emergency 911 or E911 functionality within cellular and wireless communication systems is becoming more extensive as legislative requirements are requiring and mandating such additional capabilities. It is well recognized that traditional 911 services offer the desired emergency time-saving benefits by immediately providing, to emergency personnel, the location or site of an emergency based on the call. Unlike a house or other structure where a fixed phone and associated telephone number are located, wireless systems utilize mobile units. Therefore, location identification for such mobile units is a mandated requirement for cellular systems
Location identification and location measurement within a wireless system is utilized to determine the geographical position of a cellular handset, such as a telephone, or of other cellular or wireless equipment used in initiating a 911 call. The determined location is then used by the emergency system to dispatch the necessary services (e.g. medical, fire, etc.) to the location or site. Within a wireless system, such as GSM systems, the location of a particular handset or device is determined by measuring the timing associated with various base stations in proximity to the handset. The timing of the base stations with respect to the handset is then utilized to pinpoint the location of that handset.
However, in a GSM system, the timing parameters associated with each of the various base stations will differ between the base stations because the GSM base stations are asynchronous. To address this situation, a sensor antenna is utilized to measure the timing differences of all the base stations. The sensor antenna is located in a geographically known position. With that known position and the measured timing differences for the various base stations, the location of a handset may be determined within the system.
Generally, the sensor antennas and their hardware, collectively referred to as Location Measurement Units, or LMUs, are positioned at established locations, such as on buildings. As such, the operators of the wireless systems and the owners of the antennas must often make the necessary arrangements with a building owner and must pay the required rent for the building space. For cost savings, maintenance efficiency, and other reasons, the antenna owners would prefer to mount, or co-locate, the LMU sensor antenna with an existing base station. However, such co-location has certain drawbacks which make the timing determinations difficult.
Specifically, the signal which is received by the sensor antenna, from the co-located base station antenna is significantly stronger than the signal received from the other base stations. The strong signal, in turn, will prevent the LMU receiver circuitry from performing properly to determine the timing parameters.
Therefore, it is desirable to reduce costs associated with having additional sites just for location measurement equipment, by providing co-location of such equipment with an existing base station. Furthermore, it is desirable to provide such co-location while ensuring that the LMU operates properly for location determination.